Controlling apparatus for introduction air into an exhaust pipe of an internal combustion engine

ABSTRACT

In an apparatus for controlling the introduction of air into an exhaust pipe of an internal combustion engine in which air is introduced from the intake side to the exhaust side to improve the efficiency of purifying exhaust gases, to prevent a decline in the purification efficiency of a catalyst in a state in which the exhaust gas temperature immediately after starting is low. A control valve 11 is provided in an air introducing pipe 9 for introducing air from the intake side to the exhaust side, and the control valve 11 is set in a shut-off state during starting or during starting and a predetermined time duration immediately after starting.

This is a division of application Ser. No. 08/463,634 filed Jun. 6, 1995now U.S. Pat. No. 5,566,549, which is a divisional of application Ser.No. 08/078,465 filed on Jun. 18, 1993 (U.S. Pat. No. 5,493,858).

BACKGROUND OF THE INVENTION

This invention relates to an apparatus for controlling the introductionof air into an exhaust pipe, for introducing air into an exhaust pipe ofan internal combustion engine so as to purify exhaust gases.

A catalyst is generally provided in an exhaust passage so as to purifyexhaust gases from an internal combustion engine. Immediately after thestarting of an internal combustion engine in which the catalysttemperature is low and purification efficiency is low, it has been theconventional practice to introduce air into an exhaust pipe upstream ofthe catalyst so as to promote the oxidation of HC, CO and the like inthe catalyst, thereby accelerating the temperature rise of the catalystand enhancing the purification efficiency.

FIG. 46 shows a configuration of a conventional apparatus forcontrolling the introduction of air into an exhaust pipe of an internalcombustion engine, in which reference numeral 1 denotes an internalcombustion engine; 2, a transmission; 3, an intake pipe; 4, an exhaustpipe; 5, a catalyst disposed in the exhaust pipe 4; 6, a throttle valvedisposed in the intake pipe 3; 7, an air cleaner disposed in an inletportion of the intake pipe 3; 8, an air pump mounted on the internalcombustion engine 1; 9, an air introducing pipe for introducing air tothe exhaust pipe 4 upstream of the catalyst 5 by means of the air pump8; and 10, a check valve disposed in the air introducing pipe 9 forpreventing the reverse flow of exhaust gases from the exhaust pipe 4.

Next, a description will be given of the operation of the conventionalapparatus. The air pump 8 introduces air into the exhaust pipe 4 via theair introducing pipe 9 in correspondence with the rotation of theinternal combustion engine 1, and the air introduced to the interior ofthe exhaust pipe 4 reacts with exhaust gas components CO and HC in theexhaust pipe 4 and in the catalyst 5 and converts the same into H₂ O andCO₂, thereby effecting the purification of the exhaust gases. Theintroduction of air into the exhaust pipe 4 is started simultaneouslywith the on operation of an unillustrated starter switch, as shown inFIG. 47. The amount of air introduced at this time is substantiallyfixed in terms of time, as shown in FIG. 48, and the temperature of theintroduced air is that of the atmospheric air.

FIG. 49 shows a configuration of another conventional apparatus, inwhich reference numeral 11 denotes a control valve disposed in the airintroducing pipe 9 for adjusting the amount of air to be introduced; 15,a heater for heating the air passing through the air introducing pipe 9;16, a relief valve attached to the control valve 11; and 12, acontroller for controlling the control valve 11 and the heater 15. Theother configuration is the same as that of FIG. 46.

Next, a description will be given of the operation of the conventionalapparatus shown in FIG. 49. At the same time as an unillustrated keyswitch is turned on, the control valve 11 opens the passage by beingcontrolled by the controller 12. While the internal combustion engine iscranking (when the starter switch is turned on), the air pump 8 isdriven by the internal combustion engine 1 and introduces the air intothe exhaust pipe 4 via the air introducing pipe 9, the control valve 11,the heater 15, and the check valve 10. The air introduced into theexhaust pipe 4 reacts with the exhaust gas components HC and CO in theexhaust pipe 4 and the catalyst 5, thereby effecting the purification ofthe exhaust gases. FIG. 50 shows a chart of operation at this time, inwhich the starter switch is also turned on simultaneously as the keyswitch is turned on, the internal combustion engine 1 also starts torotate simultaneously therewith and drives the air pump 8, therebyintroducing an amount of air corresponding to its number of revolutionsinto the exhaust pipe 4. At this time, the air is heated by the heater15, and the temperature of the air at the outlet of the heater 15changes with time, as shown in FIG. 51.

In addition, FIG. 52 shows still another conventional apparatus, inwhich reference numeral 8a denotes an air pump of an electricallycontrolled type disposed in the air introducing pipe 9; and 22, an airflow sensor for measuring the amount of air intake. The operation issimilar to that of the above-described conventional apparatuses.

FIG. 53 shows a configuration of a further conventional apparatus, inwhich reference numeral 46 denotes an air-fuel ratio sensor disposed inthe exhaust pipe 4 for detecting the air-fuel ratio of the exhaustgases, and the other configuration is the same as described above.Although the operation is similar to that described above, the air-fuelratio sensor 46 detects the air-fuel ratio of an air-fuel mixture of theintroduced air and the exhaust gases at the time of the introduction ofthe air, and is capable of controlling the air-fuel ratio on the basisof it.

The conventional apparatuses for controlling the introduction of airinto an exhaust pipe of an internal combustion engine are arranged asdescribed above, and the normal-temperature air is introduced into theexhaust pipe 4 immediately after starting when the exhaust gastemperature is low, so that there has been a problem in that thetemperature of the exhaust gases is further lowered by the introducedair, thereby resulting in a decline in the efficiency of purifying theexhaust gases in the catalyst 5.

In addition, since the air is introduced into the exhaust pipe 4simultaneously as the starter switch is turned on, the air passesthrough the interior of the heater 15 before the heater 15 reaches apredetermined temperature, and the speed of temperature rise of theheater 15 is delayed. Hence, there has been a problem in that theefficiency of purifying the exhaust gases in the catalyst 5 declines.

Furthermore, the amount of air introduced is constant irrespective ofthe operating condition of the engine and the type and condition of thecatalyst 5, so that there has been a problem in that an optimumpurification efficiency cannot be attained.

In addition, since the high temperature of the exhaust gases from theexhaust pipe 4 acts on the check valve 10, the heater 15, and thecontrol valve 11 disposed in the air introducing pipe 9, it is difficultfor these members to operate properly for long periods of time, which inthe long run resulted in the decline in the purification efficiency.

With the conventional apparatuses, the introduction of air is commencedsimultaneously with starting and, as shown in FIG. 54, the introductionof the air into the exhaust pipe 4 is continued even after the passingof a point of time (point A) when the catalyst inlet temperature (solidline) and the catalyst outlet temperature (dotted line) in the exhaustpipe 4 agree with each other. As a result, the temperature rise of thecatalyst 5 becomes saturated, so that a further improvement in theefficiency of purification by the catalyst 5 is hampered. At the sametime, the condition becomes one in which oxygen is in a state ofoversupply, and the action of reducing nitrogen oxides by means of thecatalyst 5 declines, so that there has been a problem in that the amountof nitrogen oxides emitted increases.

In addition, since the air is introduced to the upstream side of theair-fuel ratio sensor 46, there has been a problem in that the air-fuelratio of the exhaust gases alone cannot be detected accurately, therebymaking it impossible to effect fuel control accurately.

SUMMARY OF THE INVENTION

This invention has been effected to overcome the above-describedproblems, and its object is to obtain an apparatus for controlling theintroduction of air into an exhaust pipe of an internal combustionengine, which is capable of enhancing the efficiency of the exhaust gaspurification reaction in the exhaust pipe and the catalyst, of reducingthe amount of nitrogen oxides emitted, and of accurately conducting fuelcontrol.

The apparatus for controlling the introduction of air into an exhaustpipe of an internal combustion engine in accordance with this inventioncomprises: means for sending air to the exhaust side via an airintroducing pipe; and controlling means for stopping the introduction ofthe air to the exhaust side during the starting of the internalcombustion engine or during starting and a predetermined time durationafter starting.

In addition, the apparatus for controlling the introduction of air intoan exhaust pipe of an internal combustion engine comprises: heatingmeans for heating the air introduced into the air introducing pipe; andcontrolling means for stopping the introduction of the heated air to anexhaust side during starting or during a predetermined time durationafter starting.

In addition, the apparatus for controlling the introduction of air intoan exhaust pipe of an internal combustion engine comprises: heatingmeans for heating the air introduced into the air introducing pipe; andcontrolling means for starting the introduction of the heated air intothe exhaust pipe after a predetermined time duration subsequent to thestarting of the engine and for varying the amount of the air introducedat a predetermined time interval.

In addition, the apparatus for controlling the introduction of air intoan exhaust pipe of an internal combustion engine comprises: heatingmeans disposed between the catalyst in the exhaust pipe and a connectingportion of the air introducing pipe so as to heat exhaust gases and theair introduced from the intake side.

In the apparatus for controlling the introduction of air into an exhaustpipe of an internal combustion engine, the heating means in the exhaustpipe is operated for a predetermined time duration even after thestopping of the engine.

The apparatus for controlling the introduction of air into an exhaustpipe of an internal combustion engine comprises: heating means forheating the air introduced into the air introducing pipe; andcontrolling means for varying the amount of air introduced into theexhaust pipe at a predetermined time interval.

In the apparatus for controlling the introduction of air into an exhaustpipe of an internal combustion engine, at least one of a time intervalat which the air introduced into the exhaust pipe is varied, the amountof variation, and the amount of heating by the heating means is variedin accordance with an operational parameter of the engine.

The apparatus for controlling the introduction of air into an exhaustpipe of an internal combustion engine comprises: air heating means forheating the air introduced into the air introducing pipe; catalystheating means for heating the catalyst; and controlling means forvarying the amount of air introduced into the exhaust pipe at apredetermined time interval.

The apparatus for controlling the introduction of air into an exhaustpipe of an internal combustion engine further comprises: an exhaust-gastemperature sensor for detecting the temperature of exhaust gases and acatalyst temperature sensor for detecting the temperature of thecatalyst and controlling means for controlling the amount of air heatedand the time interval of variation thereof in accordance with one of theexhaust gas temperature and the catalyst temperature.

In the apparatus for controlling the introduction of air into an exhaustpipe of an internal combustion engine, at least one of a time intervalat which the amount of air introduced is varied, the amount ofvariation, the amount of air heated, and the amount of catalyst heatedis varied in accordance with an operational parameter of the engine.

The apparatus for controlling the introduction of air into an exhaustpipe of an internal combustion engine comprises: controlling means forstarting the introduction of the air into the exhaust pipe after apredetermined time duration subsequent to the starting of the engine andfor varying the amount of the air introduced at a predetermined timeinterval.

The apparatus for controlling the introduction of air into an exhaustpipe of an internal combustion engine comprises: an exhaust bypasspassage disposed in a portion of the exhaust pipe upstream of acatalyst; means for introducing air into the exhaust bypass passage viaan air introducing pipe; means for heating the introduced air; achangeover valve for changing over the flow of exhaust gases between theexhaust pipe and the exhaust bypass passage; and controlling means forchanging over the changeover valve in such a manner that the exhaustgases flow to the exhaust pipe before a predetermined time durationprior to the stopping of the introduction of air.

In the apparatus for controlling the introduction of air into an exhaustpipe of an internal combustion engine, the introduction of air isstarted after a predetermined time duration subsequent to the startingof the engine.

The apparatus for controlling the introduction of air into an exhaustpipe of an internal combustion engine comprises: means for detecting aheat capacity imparted to the catalyst by the exhaust gases; and meansfor starting the introduction of air to the exhaust side when the heatcapacity reaches a predetermined value.

The apparatus for controlling the introduction of air into an exhaustpipe of an internal combustion engine comprises: exhaust-gas temperaturesensors for detecting the exhaust gas temperature at an inlet and anoutlet of the catalyst; and means for stopping the introduction of airinto the exhaust pipe when the inlet temperature and the outlettemperature of the catalyst have agreed with each other or when thetemperature difference has become a predetermined value or less.

The apparatus for controlling the introduction of air into an exhaustpipe of an internal combustion engine comprises: an air-fuel ratiosensor disposed in the exhaust pipe upstream of a connecting portion ofthe air introducing pipe so as to detect an air-fuel ratio of exhaustgases; an oxygen sensor for detecting an oxygen concentration in theexhaust pipe; and controlling means for effecting fuel control andcontrol of the amount of air introduced in accordance with the outputsof the respective sensors.

The apparatus for controlling the introduction of air into an exhaustpipe of an internal combustion engine comprises: an exhaust bypasspassage disposed in a portion of the exhaust pipe upstream of acatalyst; heating means disposed in the exhaust bypass passage; achangeover valve for changing over the flow of the exhaust gases betweenthe exhaust pipe and the exhaust bypass passage; and controlling meansfor changing over the changeover valve in such a manner that the exhaustgases flow to the exhaust pipe when the introduction of air is stopped.

The apparatus for controlling the introduction of air into an exhaustpipe comprises: means for heating the air introduced into the airintroducing pipe; and controlling means for varying the amount of airintroduced into the exhaust pipe at a predetermined time interval andfor varying also the magnitude of the amount of air introduced.

The apparatus for controlling the introduction of air into an exhaustpipe comprises: an exhaust bypass passage disposed in a portion of theexhaust pipe upstream of a catalyst; means for introducing air into theexhaust bypass passage via an air introducing pipe; means for heatingthe introduced air; a changeover valve for changing over the flow ofexhaust gases between the exhaust pipe and the exhaust bypass passage;and controlling means for prohibiting the introduction of air to theexhaust bypass passage for a predetermined time duration subsequent tostarting and for operating the changeover valve before a predeterminedtime duration prior to the introduction of air so as to allow theexhaust gases to flow to the exhaust bypass passage.

In this invention, the introduction of air to the exhaust pipe is noteffected during starting or during starting and a predetermined timeduration after starting, with the result that a further decline in thetemperature of the exhaust gases whose temperature is low is prevented,and a decline in the purification efficiency of the catalyst immediatelyafter starting does not occur.

In addition, the introduction of the heated air to the exhaust pipe isprohibited during engine starting or a predetermined time duration afterstarting, so that a decline in the exhaust gas temperature due to theintroduction of the low-temperature heated air does not occur, therebypreventing a decline in the purification efficiency of the catalyst.

In addition, the heated air is introduced to the exhaust pipe after apredetermined time duration subsequent to starting, so that a decline inthe purification efficiency of the catalyst due to a drop in the exhaustgas temperature does not occur. Furthermore, the amount of heated airintroduced is varied at predetermined time intervals, and the atmosphereof the reaction system of the catalyst is alternately varied to the richside and the lean side, thereby improving the purification efficiency ofthe catalyst.

In addition, the exhaust gases and the air introduced from the intakeside are heated by the heating means disposed in the exhaust pipe, withthe result that the exhaust gas temperature increases, thereby promotingthe exhaust-gas purifying action in the exhaust pipe and the catalyst.

In addition, the heating means in the exhaust pipe is operated evenafter the stopping of the engine, and the soot adhering to the interiorof the heating means through which the exhaust gases have ceased to flowis burned.

In addition, the air introduced into the exhaust pipe is heated, and theamount of air introduced is varied at predetermined time intervals,thereby improving the purification efficiency of the catalyst.

In addition, at least one of a time interval at which the amount of airintroduced into the exhaust pipe is varied, the amount of variation, andthe amount of heating by the heating means is varied in accordance withan operational parameter of the engine. Hence, optimum purificationefficiency is obtained in accordance with the conditions of the exhaustgases and the catalyst.

In addition, the air introduced in the exhaust pipe and the catalyst areheated, and the reaction speed in the chemical reaction is accelerated.At the same time, the amount of air introduced is varied atpredetermined time intervals, thereby improving the purificationefficiency of the catalyst.

In addition, the amount of air introduced and the time interval ofvariation thereof are controlled in accordance with one of the exhaustgas temperature and the catalyst temperature. As a result, theoverheating of the catalyst is prevented, and optimum introduction ofair is effected in accordance with the operating condition of theengine.

In addition, at least one of a time interval at which the amount of airintroduced into the exhaust pipe is varied, the amount of variation, theamount of air heated, and the amount of catalyst heated is varied inaccordance with an operational parameter of the engine, so that optimumpurification efficiency is obtain in accordance with the conditions ofthe exhaust gases and the catalyst.

In addition, the introduction of air into the exhaust pipe is startedafter a predetermined time duration after engine starting, so that adecline in the purification efficiency of the catalyst due to a drop inthe exhaust gas temperature does not occur. In addition, the amount ofair introduced is varied periodically, thereby promoting the exhaust-gaspurifying action.

In addition, the exhaust gases are allowed to flow to the exhaust bypasspassage only during the introduction of air to the exhaust side, therebyalleviating the effect of the heat of the exhaust gases on the heaterand the like.

In addition, the introduction of air is started after a predeterminedtime duration subsequent to starting, so that a drop in the catalysttemperature due to the air introduced immediately after starting doesnot occur.

In addition, the heat capacity imparted by the exhaust gases to thecatalyst after engine starting is detected, the degree of activity ofthe catalyst is detected from this heat capacity, and the introductionof air to the exhaust side is started when the degree of activity hasreached a predetermined value.

In addition, the inlet temperature and outlet temperature of thecatalyst are detected, and whether or not the catalyst has assumed anactive state is determined from these temperatures, and the introductionof air to the exhaust pipe is stopped when the catalyst has assumed theactive state. As a result, the temperature rise of the catalyst ispromoted, and an increase in the amount of nitrogen oxides emitted owingto an oversupply of oxygen is prevented.

In addition, since the air-fuel ratio sensor is located in the exhaustpipe upstream of the connecting portion of the air introducing pipe, theair-fuel ratio of the exhaust gases alone is detected, so that accurateair-fuel-ratio control is carried out. In addition, the oxygenconcentration in the vicinity of the catalyst is detected by the oxygensensor, and air is introduced correspondingly in such a manner that anamount of oxygen necessary for the catalyst is obtained, therebyimproving the purification efficiency of the catalyst.

In addition, the exhaust gases are allowed to flow to the exhaust bypasspassage only during the introduction of air from the intake side to theexhaust side, so that the effect of the heat of the exhaust gases on theheater and the air introducing pipe is alleviated.

In addition, the air introduced to the exhaust pipe is heated, theamount of air introduced is varied at predetermined time intervals, andits magnitude is also varied.

In addition, the introduction of air to the exhaust side is not carriedout for a predetermined time duration after starting, so that a declinein the purification efficiency does not occur. In addition, the exhaustgases are allowed to flow to the exhaust bypass passage only during theintroduction of air to the exhaust side, thereby eliminating the effectof the heat of the exhaust gases.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram in accordance with embodiment 1 of theapparatus of this invention;

FIG. 2 is a timing chart illustrating the operation in accordance withembodiment 1 of the apparatus of this invention;

FIG. 3 is a schematic diagram in accordance with embodiment 2 of theapparatus of this invention;

FIG. 4 is a timing chart illustrating the operation in accordance withembodiment 2 of the apparatus of this invention;

FIG. 5 is a diagram of fluctuations of the outlet temperature of theheater in accordance with embodiment 2 of the apparatus of thisinvention;

FIG. 6 is a schematic diagram in accordance with embodiment 3 of theapparatus of this invention;

FIG. 7 is a diagram of variation of the amount of air introduced inaccordance with embodiment 3 of the apparatus of this invention;

FIG. 8 is a schematic diagram in accordance with embodiment 4 of theapparatus of this invention;

FIG. 9 is a waveform diagram of the operation of the heater inaccordance with embodiment 4 of the apparatus of this invention;

FIG. 10 is a schematic diagram in accordance with embodiment 5 of theapparatus of this invention;

FIGS. 11A and 11B are diagrams of variation of the amount of airintroduced in accordance with embodiment 5 of the apparatus of thisinvention;

FIG. 12 is a diagram of variation of the amount of air introduced inaccordance with embodiment 5 of the apparatus of this invention;

FIG. 13 is a diagram of variation of the amount of air introduced inaccordance with embodiment 5 of the apparatus of this invention;

FIGS. 14A and 14 are diagrams of variation of the amount of airintroduced in accordance with embodiment 6 of the apparatus of thisinvention;

FIG. 15 is a diagram of variation of the amount of air intake inaccordance with embodiment 8 of the apparatus of this invention;

FIG. 16 is a diagram of relationship between the amount of air intakeand the amount of air introduced in accordance with embodiment 8 of theapparatus of this invention;

FIG. 17 is a diagram of variation of the amount of air introduced inaccordance with embodiment 8 of the apparatus of this invention;

FIG. 18 is a diagram of relationship between the coolant temperature andthe amount of air introduced in accordance with embodiment 8 of theapparatus of this invention;

FIG. 19 is a diagram of relationship between the engine speed and theamount of air introduced in accordance with embodiment 8 of theapparatus of this invention;

FIG. 20 is a diagram of relationship between the throttle opening andthe amount of air introduced in accordance with embodiment 8 of theapparatus of this invention;

FIG. 21 is a data map of the amount of air introduced in accordance withembodiment 8 of the apparatus of this invention;

FIG. 22 is a diagram of relationship between the engine speed and theamount of heating in accordance with embodiment 9 of the apparatus ofthis invention;

FIG. 23 is a diagram of relationship between the engine speed and theamount of air introduced in accordance with embodiment 9 of theapparatus of this invention;

FIG. 24 is a diagram of relationship between the coolant temperature andthe amount of heating in accordance with embodiment 9 of the apparatusof this invention;

FIG. 25 is a diagram of relationship between the coolant temperature andthe amount of heating in accordance with embodiment 9 of the apparatusof this invention;

FIG. 26 is a diagram of relationship between the amount of air intakeand the amount of heating in accordance with embodiment 9 of theapparatus of this invention;

FIG. 27 is a diagram of relationship between the intake air temperatureand the amount of heating in accordance with embodiment 9 of theapparatus of this invention;

FIG. 28 is a diagram of relationship between the introduced airtemperature and the amount of heating in accordance with embodiment 9 ofthe apparatus of this invention;

FIG. 29 is a diagram of relationship between the throttle opening andthe amount of heating in accordance with embodiment 9 of the apparatusof this invention;

FIG. 30 is a schematic diagram in accordance with embodiment 10 of theapparatus of this invention;

FIG. 31 is a schematic diagram in accordance with embodiment 15 of theapparatus of this invention;

FIG. 32 is a schematic diagram in accordance with embodiment 16 of theapparatus of this invention;

FIG. 33 is a timing chart illustrating the operation in accordance withembodiment 16 of the apparatus of this invention;

FIG. 34 is a schematic diagram in accordance with embodiment 17 of theapparatus of this invention;

FIG. 35 is a diagram of an output of an exhaust-gas temperature sensorin accordance with embodiment 17 of the apparatus of this invention;

FIG. 36 is a schematic diagram in accordance with embodiment 18 of theapparatus of this invention;

FIG. 37 is a diagram of an output of the exhaust-gas temperature sensorin accordance with embodiment 18 of the apparatus of this invention;

FIG. 38 is a timing chart illustrating the operation in accordance withembodiment 18 of the apparatus of this invention;

FIG. 39 is a schematic diagram of an apparatus for controlling theintroduction of air into an exhaust pipe of an internal combustionengine in accordance with an embodiment 19 of this invention;

FIG. 40 is a diagram of the relationship between the amount of airintroduced and the catalyst temperature in accordance with theembodiment 19 of this invention;

FIG. 41 is a diagram of the relationship between the amount of airintroduced into the heater and the outlet temperature in accordance withthe embodiment 19 of this invention;

FIG. 42 is a diagram of the relationship between the amount of airintroduced and the amount of heat in accordance with the embodiment 19of this invention;

FIG. 43 is a timing chart for changing over the amount of air inaccordance with the embodiment 22 of this invention;

FIG. 44 is a schematic diagram in accordance with embodiment 23 of theapparatus of this invention;

FIG. 45 is a schematic diagram in accordance with embodiment 24 of theapparatus of this invention;

FIG. 46 is a schematic diagram of a conventional apparatus;

FIG. 47 is a timing chart illustrating the operation of a firstconventional apparatus;

FIG. 48 is a timing chart of the amount of air introduced in the firstconventional apparatus;

FIG. 49 is a schematic diagram of a second conventional apparatus;

FIG. 50 is a timing chart illustrating the operation of the secondconventional apparatus;

FIG. 51 is a diagram of fluctuations of an outlet temperature of aheater in the second conventional apparatus;

FIG. 52 is a schematic diagram of a third conventional apparatus;

FIG. 53 is a schematic diagram of a fourth conventional apparatus;

FIG. 54 is a diagram of an output of the exhaust-gas temperature sensorof a conventional apparatus.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Embodiment 1

Hereafter, a description will be given of the embodiments of thisinvention with reference to the drawings. FIG. 1 shows an apparatus forcontrolling the introduction of air into an exhaust pipe of an internalcombustion engine in accordance with embodiment 1, in which, as the sameas conventional art, reference numeral 1 denotes an internal combustionengine; 2, a transmission; 3, an intake pipe; 4, an exhaust pipe; 5, acatalyst disposed in the exhaust pipe 4; 6, a throttle valve disposed inthe intake pipe 3; 7, an air cleaner disposed in an inlet portion of theintake pipe 3; 8, an air pump mounted on the internal combustion engine1; 9, an air introducing pipe for introducing air to the exhaust pipe 4upstream of the catalyst 5 by means of the air pump 8; 10, a check valvedisposed in the air introducing pipe 9 for preventing the reverse flowof exhaust gases from the exhaust pipe 4, and 11, a control valvedisposed in the air introducing pipe 9 for adjusting the amount of airto be introduced. Furthermore, reference numeral 17 denotes a controllerfor controlling the control valve 11; 13, a starter switch; and 14, abattery. Next, a description will be given of the operation ofembodiment 1. During and after the starting of an internal combustionengine 1, air is supplied into an air introducing pipe 9 by means of anair pump 8. Meanwhile, the controller 17 receives an on/off signal ofthe starter switch 13 shown in (a) part of FIG. 2, and does not allowthe control valve 11 to be operated during the "on" period of thestarter switch 13, as shown in (b) part, or until the lapse of apredetermined time duration T₁ after the turning on of the starterswitch 13, as shown in (c) part. Accordingly, during this period, thecontrol valve 11 remains closed and the introduction of air into theexhaust pipe 4 is not effected, thereby making it possible to prevent adecline in the purification efficiency due to a temperature drop of theexhaust gases in the exhaust pipe 4 immediately after starting.Subsequently, the control valve 11 is opened to introduce air into theexhaust pipe 4, and during this period it is possible to improve theefficiency of purifying the exhaust gases whose temperature has risen.

It should be noted that although in embodiment 1 the control valve 11 iscontrolled by means of the controller 17, in a case where the air pump 8is of an electrically operated type, a similar effect can be obtained ifthe operation of the air pump 8 is controlled.

Embodiment 2

FIG. 3 shows a configuration of embodiment 2, in which reference numeral15 denotes a heater for heating the air passing through the airintroducing pipe 9; 16, a relief valve attached to the control valve 11;18, a controller for controlling the control valve 11 and the heater 15,and the other configuration is the same as described above.

Next, a description will be given of the operation of embodiment 2.Turning on of the starter switch 13 at the time of starting supplies thevoltage of the battery 14 to the controller 18. The controller 18operates the heater 15 as the starter switch is turned on. During andafter the starting of the internal combustion engine 1, air isintroduced into the air introducing pipe 9 in correspondence with therotation of the internal combustion engine 1 as the air pump 8 isoperated. However, as shown in (b) part of FIG. 4, since the controller18 does not open the control valve 11 for the predetermined timeduration T₁ after the turning on of the starter switch 13, air is notsupplied to the exhaust pipe 4. After the lapse of the time duration T₁,the control valve 11 is opened, so that the heated air is supplied tothe exhaust pipe 4. In this case, the air temperature at the outlet ofthe heater 15 is shown in FIG. 5 by dotted line b, and the speed oftemperature rise becomes faster than in the conventional case shown bysolid line a, with the result that the efficiency of purification at thecatalyst 5 improves.

Although, in embodiment 2, the control valve 11 is not opened for thetime duration T₁ after the turning on of the starter switch 13, asimilar effect is obtained if the control valve 11 is not opened duringstarting, i.e., during the "on" period of the starter switch 13, asshown in part (c) of FIG. 4. In addition, in a case where the air pump 8is of an electrically operated type, the air pump 8 may not be operatedduring starting or during a predetermined period after starting withoutusing the control valve 11.

Embodiment 3

FIG. 6 shows a configuration of embodiment 3, in which reference numeral19 denotes a controller for controlling the control valve 11 and theheater 15. The other configuration is the same as described above.

Next, a description will be given of the operation of embodiment 3. Atthe same time as the internal combustion engine 1 is started, air isintroduced into the air introducing pipe 9 by the operation of the airpump 8. However, the controller 19 does not turn on the control valve 11for a time duration S₁ after the starter switch 13 is turned on. Forthis reason, the amount of air introduced to the exhaust side is zerofor the time duration S₁, as shown in FIG. 7. Meanwhile, the controller19 operates the heater 15 simultaneously with starting. After the lapseof the time duration S₁ subsequent to starting, the controller 19 opensthe control valve 11, and the air introduced from the intake side issupplied to the exhaust pipe 4 via the check valve 10 and the heater 15.Accordingly, the temperature of the air supplied to the exhaust pipe 4is increased to an appropriate temperature level, and the decline in thecatalyst efficiency due to the drop in the exhaust gas temperature doesnot occur.

In addition, the amount of air introduced into the exhaust pipe 4 isvaried alternately by Q₂ and Q₃ above or below Q₁, which is set as areference, at predetermined time intervals T₂ and T₃ through control bythe controller 19. As a result, as described in 861012 "Improvement oflow-temperature activity of ternary catalysts" in JSAE Spring ConventionProceedings 861, 1986-5, the atmosphere of a reaction system in which aternary catalyst is used is changed periodically to the rich side andthe lean side, thereby making it possible to substantially improve thepurification efficiency of the catalyst. The period of T₂ +T₃ isnormally set to 1-10 Hz or thereabouts, and this period, together withQ₁ to Q₃, is set to an optimum value in accordance with the catalystbeing used.

In embodiment 3, the heated air is not introduced into the exhaust pipe4 for the time duration S₁ after the starting of the engine, but in thecase where the air pump 8 is of an electrically operated type, a similareffect is obtained if the air pump 8 is controlled by the controller 19without providing the control valve 11.

Embodiment 4

FIG. 8 illustrates a configuration in accordance with embodiment 4, inwhich reference numeral 20 denotes a controller for controlling theheater 15, and 21 denotes a key switch, the heater 15 being disposedbetween the catalyst 5 and a connecting portion of the air introducingpipe 9 in the exhaust pipe 4. The other configuration is the same asdescribed above.

Next, a description will be given of the operation of embodiment 4. Asthe internal combustion engine 1 rotates, the air pump 8 rotates, whichcauses air to be introduced into the exhaust pipe 4 via the airintroducing pipe 9. Meanwhile, the heater 15 is operated by thecontroller 20 at the same time as the starting of the engine. The airintroduced into the exhaust pipe 4 is mixed with the exhaust gases, issent to the heater 15, and is thereby heated. Accordingly, thetemperature of the gas mixture increases, so that the efficiency ofpurification of the exhaust gases in the catalyst 5 improves. Inaddition, as shown in FIG. 9, since the heater 15 is operated for thetime duration T₁ even after the key switch 21 is turned off, the heater15 maintains the heating condition, and when the engine is stopped andthe exhaust gases no longer flow through the heater 15, the sootadhering inside the heater 15 is burned. For this reason, the heater 15is capable of constantly allowing the exhaust gases to flowsatisfactorily.

Embodiment 5

FIG. 10 illustrates a configuration in accordance with embodiment 5, inwhich reference numeral 22 denotes an air-flow sensor for detecting theamount of air taken into the internal combustion engine 1; 23, arevolution sensor for detecting the number of revolutions of acrankshaft of the internal combustion engine 1; 24, a coolanttemperature sensor for detecting the temperature of a coolant forcooling the internal combustion engine 1; 25, an oil temperature sensorfor detecting the temperature of oil ill the internal combustion engine1 and the transmission; 26, an intake manifold pressure sensor fordetecting the downstream negative pressure of the throttle valve 6; 27,an intake-air temperature sensor for detecting the intake-airtemperature of the atmospheric air; 28, an atmospheric pressure sensorfor detecting the atmospheric pressure of the outside air; 29, athrottle opening sensor for detecting the opening of the throttle valve6; 30, an exhaust pressure sensor for detecting the pressure of exhaustgases flowing through the exhaust manifold; 31, an exhaust-gastemperature sensor; 32, an introduced-air temperature sensor; 36, acatalyst temperature sensor; and 33, a controller to which variousparameters of the internal combustion engine 1 are inputted, and whichperform various determinations and calculations in accordance with theseparameters, so as to control the heater 15 and the control valve 11.

Next, a description will be given of the operation of embodiment 5. Asthe internal combustion engine 1 rotates, the air pump 8 rotates, whichcauses air to be introduced into the exhaust pipe 4 via the airintroducing pipe 9. The amount of air introduced at this time is variedalternately to the lean side and the rich side at predetermined timeintervals T₁, T₂ or T₃, T₄, as shown in FIGS. 11(a) and 11(b), bycontrolling the control valve 11 by means of the controller 33. Thepurification efficiency improves through such variations, as describedabove. In addition, the introduced air is heated by the heater 15,whereby the purification efficiency also improves. The time intervals T₁to T₄ are set to be periods of 1 to 10 Hz or thereabouts, and they arevaried in accordance with the type, amount, and condition of thecatalyst 5 used.

Although, in embodiment 5, the amount of air introduced is varied at thetime intervals T₁ to T₄, by changing the ratio between a time intervalT₆ or T₈ when the amount of air introduced is large and a time intervalT₅ or T₇ when it is small, i.e., the duty, as shown in FIGS. 12 and 13,it is possible to allow the average flow rate to assume an optimum valuein accordance with the component, amount, and condition of the catalyst5 and the operating condition of the internal combustion engine 1. Inaddition, although the air from the intake side is introduced from theintake manifold located downstream of the throttle valve 6 by means ofthe air pump 8, the air may be introduced from the upstream of thethrottle valve 6, or from the upstream of the air flow sensor 22, or byproviding an introducing port separate from the air cleaner 7.Furthermore, as the control valve 11, it is possible to use a linearsolenoid for controlling the opening by means of a duty signal, a dutysolenoid for controlling the flow rate by means of an on-off signal, avalve which is controlled by a stepping motor, a DC motor, or anultrasonic motor, or a valve for controlling the opening throughnegative pressure.

Embodiment 6

Although, in embodiment 5, a case has been shown in which the timeintervals are varied, an arrangement may be provided such that theamplitude of variation (amount of variation) of the introduced air ismade variable so as to assume an optimum value in accordance with thecomponent, amount, and condition of the catalyst 5 and the operatingcondition of the internal combustion engine 1. That is, there is a casewhere only the amplitude of variation is changed in accordance with thecapacity of the catalyst 5, as shown in FIG. 11(a) and 11(b), and thereis a case where both the value when the amount of air introduced islarge and the value when it is small are changed in accordance with thecondition of the catalyst 5 and the operating condition of the internalcombustion engine 1, as shown in FIGS. 14(a) and 14(b), so as to set thevalues to optimum values.

Embodiment 7

By combining the embodiments 5 and 6, both the time intervals ofvariation of the amount of air introduced and the amplitude of variationthereof are changed and set more optimally in accordance with thecomponent, amount, and condition of the catalyst 5 and the operatingcondition of the internal combustion engine 1.

Embodiment 8

By changing the time intervals of variation of the amount of airintroduced and the amount of variation thereof in accordance with theoperational parameters of the internal combustion engine 1, morefinely-tuned control becomes possible, and the purification of exhaustgases in an ideal manner can be implemented. As the operationalparameters, it is possible to cite, among others, the exhaust gastemperature, catalyst temperature, exhaust pressure, engine speed,amount of intake air, throttle opening, intake manifold pressure,coolant temperature, oil temperature, intake air temperature, andatmospheric pressure. A description will be given of a case where if,for instance, the amount of air taken into the engine is Q_(A) and theamount of air introduced into the exhaust pipe 4 is Q_(B),

    Q.sub.B =K Q.sub.A                                         (1)

and the amount of air introduced Q_(B) is varied in accordance with theamount of intake air Q_(A).

When Q_(A) increases with time, as shown in FIG. 15, Q_(B) also needs tobe increased correspondingly. At this time, if Q_(A) and Q_(B) are in alinear relationship, as shown in FIG. 16, it suffices if Q_(B) is set asin FIG. 17. The amount of intake air Q_(A) may be measured by the airflow sensor 22, but a value equivalent to the amount of intake air maybe determined by the throttle opening sensor 29, the intake manifoldpressure sensor 26, or the like. In particular, since the throttleopening makes it possible to speedily ascertain the accelerating ordecelerating behavior of the vehicle driver, Q_(B) can be changedspeedily in response to a sudden change in the operating condition ofthe engine.

FIG. 18 shows a relationship between an engine coolant temperature T_(W)and the amount of air introduced Q_(B). When the coolant temperatureT_(W) is low, a rich air-fuel mixture is normally supplied to theengine, the efficiency of purifying unburnt exhaust gas components canbe improved by increasing the amount of air introduced Q_(B). However,since components of the exhaust gases actually change in various waysdue to the setting of the air-fuel ratio and the like, it is possible toobtain an optimum amount of air introduced Q_(B) by taking variousconditions into account.

FIG. 19 shows the relationship between the engine speed and Q_(B), andQ_(B) is increased on the assumption that an increase in the enginespeed N_(e) entails an increase in the amount of intake air per time. Ina region of very high revolution, the amount of heat generated due tooxidation reaction in the catalyst 5 becomes excessively large, so thatQ_(B) is reduced. FIG. 20 shows the relationship between a throttleopening θ and Q_(B).

FIG. 21 shows a case where a parameter for determining Q_(B) is providedas map values with respect to two parameters, the engine speed N_(e) andthe amount of intake air Q_(A), and by using coefficients K₁ to K₉ ofnine zones, Q_(B) is determined on the basis of

    Q.sub.B =K.sub.n *Q.sub.A                                  (2)

In addition, Q_(B) may be determined irrespective of Q_(A) by usingcoefficients K₁ to K₉. That is, Q_(B) may be made equal to K_(n).Furthermore, by assuming that T_(e) is the exhaust gas temperature,T_(o) is the oil temperature, P_(b) is the atmospheric pressure, T_(a)is the intake air temperature, P_(i) is the intake manifold pressure,T_(c) is the catalyst temperature, T₁ is the temperature of theintroduced air, and functions using them as variables are FQ_(A) (X),FT_(W) (X), FN_(e) (X), Fθ(X), FT_(e) (X), FT_(o) (X), FP_(b) (X),FT_(a) (X), FP_(i) (X), FT_(c) (X), and FT₁ (X), a setting may beprovided as follows: ##EQU1##

Alternatively, the functions may be combined by multiplication asfollows: ##EQU2##

In addition, it is possible to combine addition and multiplication, orit is possible to use a function F(X₁, X₂, X₃, . . . , X_(n)) which isdetermined by two or more parameters. Although a description has beengiven of the case where the amount of air introduced Q_(B) is varied inaccordance with the parameters of the operating condition of the engine,the periodically changing time intervals and the amount of variation ofthe amount of air introduced Q_(B) may be varied in accordance with theparameters.

Embodiment 9

Although, in embodiment 8, the amount of introduced air to be controlledis varied in accordance with the operational parameters of the engine,the amount of heat to be imparted to the heater 15 may additionally bevaried in accordance with the engine parameters. For instance, in FIG.19, Q_(B) is decreased since the amount of heat generated due to theoxidation reaction in the catalyst in the region of very high revolutionbecomes excessively large. At that time, an arrangement may be providedsuch that, as shown in FIG. 22, the amount of heat in the heater 15 isreduced or cut off, and the normal-temperature air is introduced, so asto cool the catalyst 5, or, as shown in FIG. 23, an attempt may be madenot to decrease Q_(B). FIGS. 24 to 29 show examples in which the amountof introduced air heated by the heater 15 is varied in accordance withthe coolant temperature T_(W), the amount of air Q_(A) taken into theengine, the intake air temperature T_(a), and the temperature ofintroduced air T₁, respectively.

Embodiment 10

FIG. 30 shows a configuration in accordance with embodiment 10, in whichreference numeral 8a denotes an electrically operated air pump of, forinstance, a turbo type or a stroke type and driven by a DC motor; 34, acatalyst heater for heating the catalyst 5; 36, a catalyst temperaturesensor; and 35, a controller to which the various parameters of theinternal combustion engine 1 are inputted and which perform variousdeterminations and calculations in accordance with these parameters soas to control the heaters 15, 34 and the control valve 11. The otherconfiguration is the same as described above.

Next, a description will be given of the operation of embodiment 10. Theair which has been purified by being passed through the air cleaner 7 issucked by the air pump 8a, and is introduced into the air introducingpipe 9. The control valve 11 receives a control signal from thecontroller 35, and varies the air-fuel ratio alternately to the leanside and the rich side at time intervals T₁ and T₂. The ratio between T₁and T₂ and the period T are stored in advance in the memory in thecontroller 35. For instance, T₁ :T₂ =1:1, T=0.1-5.0 sec. It should benoted that the time intervals and the period may be set as T₃, T₄, and Tin accordance with the operating condition of the internal combustionengine 1, as shown in FIG. 11(b).

The introduced air controlled by the controller 11 is supplied to theheater 15, is heated to a predetermined temperature, and is introducedinto the exhaust pipe 4 upstream of the catalyst 5 via the check valve10. In addition, the catalyst heater 34 is energized through control bythe controller 35 at the same time as the internal combustion engine 1is started, so as to heat the catalyst 5. Since an upper limit of theheat resistance temperature of the catalyst 5 is 900° C., if thetemperature exceeds that level, the catalyst 5 becomes deteriorated. Forthis reason, the energization of the catalyst heater 34 is stopped afterthe lapse of a predetermined time (e.g. 200 sec.). Thus, in embodiment10, the amount of air introduced is varied at predetermined timeintervals, and it is possible to improve the efficiency of purificationof the catalyst 5. Moreover, the introduced air and the catalyst 5 areheated, so that the temperatures of the mixed air and the catalyst 5 areincreased, thereby making it possible to improve the purificationaction.

Although, in embodiment 10, the time intervals at which the amount ofair introduced is varied are set to be T₁ to T₄, the time intervals maybe set to be T₅ to T₈, as shown in FIGS. 12 and 13. In addition, as forthe portion of the air intake side from which the introduced air is tobe introduced or the type of control valve 11 to be adopted,modifications similar to those of embodiment 5 are conceivable.

Embodiment 11

Although, in embodiment 10, the time intervals are varied periodically,an arrangement may be provided such that the amplitude of variation(amount of variation) of the amount of air introduced is made variable,and is set to be an optimum value in accordance with the component,amount, and condition of the catalyst 5 and the operating condition ofthe engine. In this case, modifications are made in the same way as inembodiment 6, as in FIGS. 11 and 14.

Embodiment 12

Although, in embodiments 10 and 11, the time intervals at which theamount of air introduced is varied or the amount of variation is varied,in embodiment 12, the amount of air introduced by means of the controlvalve 11 and the time intervals of variation thereof are controlled inaccordance with an output of at least one of the output of theexhaust-gas temperature sensor 31 for detecting the temperature ofexhaust gases and the output of the catalyst temperature sensor 36 fordetecting the temperature of the catalyst 5. As a result, in addition tothe above-described advantages, it is possible to prevent thedeterioration of the catalyst 5 due to overheating. At the same time, itis possible to effect optimum control of the amount of air introduced inaccordance with the operating condition of the engine, and to improvethe action of purifying exhaust gases irrespective of the operatingcondition.

Embodiment 13

In embodiment 13, the amount of air introduced, the time intervals atwhich it is varied, and the amount of variation are varied in accordancewith the operational parameters of the internal combustion engine 1. Asa result, it is possible to effect finely-tuned control and to implementpurification of exhaust gases in an ideal manner. Since this control iscarried out in a manner similar to embodiment 8, a description thereofwill be omitted.

Embodiment 14

Although, in embodiment 13, the amount of introduced air to becontrolled is varied in accordance with the operational parameters ofthe engine, the amounts of heat to be imparted to the heaters 15 and 34may additionally be varied in accordance with the engine parameters. Forinstance, in FIG. 19, the amount of air introduced Q_(B) is decreasedsince the amount of heat generated due to the oxidation reaction in thecatalyst 5 in the region of very high revolution becomes excessivelylarge. At that time, an arrangement may be provided such that, as shownin FIG. 22, the amounts of heat in the heaters 15 and 34 are reduced orcut off, and the normal-temperature air is introduced, so as to cool thecatalyst 5, or, as shown in FIG. 23, an attempt may be made not todecrease Q_(B). FIGS. 24 to 29 show examples in which the amount ofintroduced air heated and the amount of catalyst heated are varied inaccordance with the engine parameters.

Embodiment 15

FIG. 31 shows a configuration in accordance with embodiment 15, in whichreference numeral 37 denotes a controller for controlling the controlvalve 11, and the other configuration is the same as described above.

Next, a description will be given of the operation of embodiment 15. Theair is introduced into the air introducing pipe 9 through the operationof the air pump 8 at the same time as the internal combustion engine 1is started. However, the controller 37 does not turn on the controlvalve 11 for the time duration S₁ after the turning on of the starterswitch 13, as shown in FIG. 7. For this reason, the amount of airintroduced to the exhaust side is zero for the time duration S₁. Afterthe elapse of the time duration S₁ subsequent to starting, thecontroller 37 sets the control valve 11 in the open state, and the airintroduced from the intake side is supplied to the exhaust pipe 4 viathe check valve 10. Accordingly, the temperature of the low-temperatureexhaust gases immediately after starting is prevented from becominglower as a result of mixing in of the low-temperature air from theintake side, and a decline in the purification efficiency of thecatalyst is prevented. The time duration S₁ assumes a value of severalto several dozen seconds. In addition, the amount of air introduced intothe exhaust pipe 4 is varied alternately by Q² and Q³ above or below Q₁,which is set as a reference, at predetermined time intervals T₂ and T₃by controlling the control valve 11, thereby making it possible toimprove the purification efficiency of the catalyst 5.

It should be noted that, in embodiment 15 as well, in a case where theair pump 8 is of an electrically operated type, the above-describedcontrolling operation can be effected by controlling the air pump 8without providing the control valve 11.

Embodiment 16

FIG. 32 shows a configuration in accordance with embodiment 16, in whichreference numeral 38 denotes an exhaust bypass passage provided in aportion of the exhaust pipe 4 upstream of the catalyst 5, wherein theair introducing pipe 9 whose one end is connected to the intake side hasanother end connected to this exhaust bypass passage 38. Referencenumeral 39 denotes a changeover valve for changing over the flow ofexhaust gases emitted from the internal combustion engine 1 between theexhaust pipe 4 side and the exhaust bypass passage 38 side; 40, a linkmechanism for the changeover valve 39; 41, an actuator for actuating thechangeover valve 39 via the link mechanism 40; and 42, a controller forcontrolling the heater 15 and the actuator 41.

Next, a description will be given of the operation of embodiment 16 withreference to FIG. 33. The air is introduced into the air introducingpipe 9 by means of the air pump 8 at the same time as the internalcombustion engine 1 is started. The controller 42 detects startingthrough the operation of the starter switch 13, and operates the heater15. In a short time, the changeover valve 39 is operated on the basis ofa command from the controller 42 via the actuator 41 and the linkmechanism 40, and is changed over in such a manner as to allow theexhaust gases to flow to the exhaust bypass passage 38. After the timeduration T₄ subsequent to the operation of this changeover valve 39,i.e., after the time duration T₁ subsequent to starting, the controller42 opens the control valve 11, so that air passes through the checkvalve 10, is heated by the heater 15, and is introduced to the exhaustbypass passage 38. After the control valve 11 is opened for the timeduration T₂, the control valve 11 is closed again.

As a result, the exhaust gases are mixed with the heated air, and the HCand CO components are efficiently purified in the exhaust bypass passage38 and the catalyst 5. In addition, the energization of the heater 15 isstopped before the time duration T₃ prior to the closing of the controlvalve 11, whereas the changeover valve 39 is operated and is changedover before the time duration T₅ prior to the closing of the controlvalve 11 in such a manner as to allow the exhaust gases to flow to theexhaust pipe 4. Accordingly, while the air is not being introduced, theexhaust gases do not flow through the exhaust bypass passage, so thatthe effect of the heat of the exhaust gases upon the heater 15 and thelike is alleviated. In addition, since the introduction of air is noteffected for a predetermined time duration after starting, a declinedoes not occur in the purification efficiency due to the decline in thecatalyst temperature immediately after starting.

It should be noted that in a case where the air pump 8 is of anelectrically operated type, the air introduction control can be effectedby means of the air pump 8 even if the control valve 11 is not provided.In addition, although the changeover valve 39 is disposed on the inletside of the exhaust bypass passage 38, the changeover valve 39 may bedisposed on the outlet side thereof.

Embodiment 17

FIG. 34 shows a configuration in accordance with embodiment 17, in whichreference numeral 43 denotes a controller for controlling the controlvalve 11 upon receipt of signals from the exhaust-gas temperature sensor31 and the starter switch 13. The other configuration is the same asdescribed above.

Next, a description will be given of the operation of embodiment 17.Exhaust gases pass through the exhaust pipe 4 and the catalyst 5 at thesame time as the internal combustion engine 1 is started. Theexhaust-gas temperature sensor disposed in the vicinity of an inlet ofthe catalyst 5 detects the temperature of the exhaust gases, anddelivers an output shown at a in FIG. 35(a) to the controller 43. Atthis time, the exhaust gas temperature at an outlet of the catalyst 5 isshown at b in FIG. 35(a). Upon receipt of the on signal from the starterswitch 13, the controller 43 integrates the output of the exhaust-gastemperature sensor 31 as shown in FIG. 35(b), detects the heat capacityimparted to the catalyst 5, and determines the degree of activity of thecatalyst 5. When the integrated value becomes α, the controller 43 opensthe control valve 11, and introduces the air from the intake side intothe exhaust pipe 4, as shown in FIG. 35(c). The predetermined value α isset in advance in correspondence with the catalyst 5. Thus, inembodiment 17, the heat capacity imparted to the catalyst 5 is detected,the degree of activity of the catalyst 5 is determined from this heatcapacity, and the introduction of air is effected after the degree ofactivity reaches the predetermined value, thereby making it possible toimprove the purification efficiency of the catalyst 5.

Although, in embodiment 17, the heat capacity imparted to the catalyst 5is detected from the exhaust gas temperature, the heat capacity may bedetected from the amount of intake into or exhaust from the engine andthe exhaust gas temperature. In addition, in the case where the air pump8 is of an electrically operated type, the air introduction control maybe effected by controlling the air pump 8 without providing the controlvalve 11.

Embodiment 18

FIG. 36 shows a configuration in accordance with embodiment 18, in whichreference numeral 8 denotes the air pump driven by the rotation of theinternal combustion engine 1; 11, the control valve for duty controlusing an electromagnetic solenoid; 31, the exhaust-gas temperaturesensor for detecting the temperature of the exhaust gases at the inletof the catalyst 5; 44, an exhaust-gas temperature sensor for detectingthe temperature of the exhaust gas at the outlet of the catalyst 5; and45, a controller for receiving outputs from the exhaust-gas temperaturesensors 31 and 44 and sending a control signal S₁ to the control valve11.

Next, a description will be given of the operation of embodiment 18.FIG. 37 shows changes in the temperature at the inlet and outlet of thecatalyst 5 when the engine is accelerated after starting and steadyrunning is effected, wherein the solid line indicates the inlettemperature, while the dotted line shows the outlet temperature, a pointof intersection of the two lines being A. In addition, FIG. 38 shows theamount of air introduced, the control signal S₁, and the operation ofthe starter switch.

The air which has passed through the air cleaner 7 is sucked by means ofthe air pump 8, and is supplied to the control valve 11. At the sametime as the starter switch is turned on, the control valve 11 receivesthe control signal S₁ from the controller 45 and is thereby set in theopen state, so that the introduction of air into the exhaust pipe 4 isstarted. As for the amount of air introduced Q, a fixed amount isintroduced in accordance with the operating condition of the engine, asshown in FIG. 38(a). It should be noted that the amount of airintroduced may be changed at predetermined time intervals.

At this time, the introduced air is introduced into the exhaust pipe 4via the check valve 10, is mixed with the exhaust gases emitted from theinternal combustion engine 1, is sent to the catalyst 5, and undergoesoxidation and reduction reaction to generate heat in the catalyst 5. Asa result, the temperature of the catalyst 5 increases, and the exhaustgas temperature at the outlet side thereof increases over the exhaustgas temperature at the inlet side thereof. Namely, the temperature ofthe exhaust gases before and after the catalyst 5 increases with atendency such as the one shown in FIG. 37. Accordingly, both the inlettemperature and the outlet temperature are detected by the exhaust-gastemperature sensors 31 and 44, the detected values are sent to thecontroller 45, and the controller 45 compares the two detected values.When the detected values agree with each other (at point A) or when thetemperature difference becomes a predetermined value or less, adetermination is made that the catalyst 5 has been set in an activatedstate, so that the control valve 11 is set in the closed state to stopthe introduction of air. As a result, the temperature rise afteractivation of the catalyst 5 is promoted, thereby making it possible tofurther improve the purification efficiency and to reduce the amount ofemission of the nitrogen oxides.

Although, in embodiment 18, the introduction of air is controlled bycontrolling the control valve 11, in a case where the air pump 8 is of aturbo type or a stroke type which incorporates a DC motor and is drivenby a DC power supply, the air introduction control can be effected bycontrolling the air pump 8.

Embodiment 19

FIG. 39 shows an embodiment of this invention, in which referencenumeral 180 denotes a temperature detector for detecting the temperatureof the catalyst.

A description will be given of the operation of this invention withrespect to the embodiment shown in FIG. 39. At the same time as thestarting of the internal combustion engine or after a predetermined timeduration subsequent to starting, the air pump is operated by acontroller 140 and discharges air. At this time, the controller 140outputs an air pump control output in such a manner as to cause the airpump 8 to discharge a maximum amount of air.

In addition, in order for the controller 140 to deliver an output foroperating a heater relay 170 at the same time as the starting of theengine, an electric current is supplied to a heater 15 via the heaterrelay 170.

Subsequently, when the temperature of the catalyst is detected by thetemperature detector 180 and a predetermined temperature is reached, thecontroller 140 changes the state for controlling the operation of theair pump 8 from the state in which the air pump 8 discharges the maximumamount of air to control in which the air pump 8 discharges apredetermined amount of air necessary for the catalyst.

Furthermore, FIG. 40 is a diagram illustrating an amount of air to bechanged in accordance with the catalyst temperature. The arrangementprovided is such that up to T1 from the starting of the engine, theaforementioned amount of air (Q1 l/min in FIG. 40) is introduced, andafter T1 a predetermined amount of air (Q2 l/min in FIG. 40) necessaryfor the catalyst is introduced.

The amount of heat which can be imparted to the catalyst through thecontrol of the aforementioned air pump and heater is shown in FIG. 41.As a characteristic of the heater, there is a tendency that thetemperature of the air outputted from heaters, in which the capacitiesof the heaters and the electric power imparted to the heaters areidentical, is proportional to an increase in the flow rate, and thetemperature does not drop. As a result, the amount of heat obtained froma heater can be expressed by the following formula:

    amount of heat=flow rate×(heater outlet temperature-heater inlet temperature)

As shown in FIG. 42, the amount of heat (Ha) when the flow rate is ashows an amount of heat obtainable from a heater in a conventionalapparatus, while the amount of heat (Hb) when the flow rate is b showsan amount of heat obtainable from this invention.

As described above, the amount of air introduced into the heater isincreased after the starting of the engine, and the amount of air ischanged to an amount necessary for the reaction of the catalyst when thecatalyst temperature reaches a predetermined temperature, whereby itbecomes possible to increase the amount of heat which can be imparted tothe catalyst, thereby making it possible to accelerate an increase inthe catalyst temperature and improve the efficiency of purification ofthe exhaust gases.

Embodiment 20

Although in the above-described embodiment the temperature detector isdisposed in the catalyst to detect the temperature of the catalyst, asimilar effect is obtained if the temperature detector detects theexhaust gas temperature at the catalyst outlet or in the exhaust pipedownstream of the catalyst.

Embodiment 21

Although in the above-embodiments the temperature of the catalyst or theexhaust gas temperature downstream of the catalyst is detected, a pointof time for changing over the flow rate may be effected in terms of timeafter the starting of the engine or after the air is begun to beintroduced to the heater, in which case a similar effect is obtained.

Embodiment 22

Although in the above-described embodiments control is provided suchthat the amount of air introduced is changed suddenly in terms of thetemperature of the catalyst, the exhaust gas temperature, or the timeafter starting, a similar effect is obtained if the flow rate is changedin steps in predetermined ranges of the temperature of the catalyst, theexhaust gas temperature, and the time after starting.

Hereafter, a description will be given of the embodiments with referenceto FIG. 43. This drawing is a timing chart on the amount of air in acase where the air is introduced to the heater from the starting of theengine, and the amount of air introduced after a predetermined timeduration is changed over.

Next, a description will be given of the operation. Since the periodfrom t1 to t2 is a period when the activity of the catalyst has not beenfully activated, this period shows a state in which the amount of air isgradually changed with the lapse of time. In addition, during the periodup to t1 from the starting of the engine and the period subsequent tot2, control is effected to introduce the amount of air in the same wayas in embodiments 1 and 2 in which the catalyst temperature is detectedor the exhaust gas temperature is detected.

In addition, it goes without saying that in the detection of thecatalyst temperature and the detection of the exhaust gas temperature aswell, the detection is realized by providing control in which the flowrate is introduced in accordance with the temperature within apredetermined temperature range.

Embodiment 23

FIG. 44 shows a configuration in accordance with embodiment 23, in whichreference numeral 47 denotes an air-fuel ratio sensor disposed in aportion of the exhaust pipe 4 upstream of a connecting portion of theair introducing pipe 9 and for detecting the air-fuel ratio of theexhaust gases; 48, an oxygen sensor disposed in the vicinity of theinlet or outlet of the catalyst 5 in the exhaust pipe 4 and fordetecting the oxygen concentration in the exhaust pipe 4; and 49, acontroller to which outputs of the air-fuel ratio sensor 47 and theoxygen sensor 48 are inputted so as to effect fuel control and tocontrol the control valve 11.

Next, a description will be given of the operation of embodiment 23.Starting is effected in the cool state of the internal combustion engine1, and during warming-up, the air-fuel ratio sensor 47 detects theair-fuel ratio from the exhaust gases in the exhaust pipe 4 in severaldozen seconds after starting. In addition, at the same time as starting,the air pump 8 introduces air via the air introducing pipe 9. Thecontroller 49 calculates an amount of oxygen necessary for reaction inthe catalyst 5 on the basis of an oxygen concentration signal from theoxygen sensor 48, controls the control valve 11 correspondingly, andallows the introduced air to be introduced into the exhaust pipe 4 sothat the necessary amount of oxygen can be obtained. Furthermore, thecontroller 49 calculates an appropriate amount of fuel in correspondencewith the output from the air-fuel ratio sensor 47, and controls anunillustrated injector correspondingly, thereby effecting fuel control.

Although, in embodiment 23, a mechanical air pump 8 which is driven bythe rotation of the internal combustion engine 1 is used, it is possibleto use an electrically operated one, in which case the control valve 11may be omitted. In addition, although the fuel control and theintroduced-air-amount control are effected by the identical controller49, these two types of control may be effected by separate controllers.

Embodiment 24

FIG. 45 shows a configuration in accordance with embodiment 24, in whichreference numeral 50 denotes a controller for controlling the heater 15,the control valve 11, and the actuator 41, the heater 15 being disposedin the exhaust bypass passage 38. The other configuration is the same asFIG. 32.

Next, a description will be given of the operation of embodiment 24. Atthe same time as the internal combustion engine 1 is started, air isintroduced into the exhaust bypass passage 38 via the air introducingpipe 9, the control valve 11, and the check valve 10 through theoperation of the air pump 8. In addition, as the starter switch 13 isturned on, the controller 50 controls the control valve 11, the heater15, and the actuator 41, and the air introduced into the exhaust bypasspassage 38 is heated by the heater 15. Meanwhile, the changeover valve39 is set in the illustrated state by the actuator 41 via the linkmechanism 41, and the exhaust gases emitted from the internal combustionengine 1 are not introduced to the exhaust pipe 4 and are introduced tothe exhaust bypass passage 38, are mixed with the introduced air, and isheated by the heater 15, so that the HC and CO components contained inthe exhaust gases are purified in the exhaust bypass passage 38 and thecatalyst 5. On the other hand, when the control valve 11 is closed bythe controller 50, the introduction of air to the exhaust side isstopped, and the changeover valve 39 is changed over in such a manner asto allow the exhaust gases to flow through the exhaust pipe 4.Accordingly, since the exhaust gases flow through the exhaust-gas bypasspassage 38 only when they are necessary, the effect of the heat of theexhaust gases on the heater 15 and the air introducing pipe 9 can bealleviated.

Although, in embodiment 24, a mechanical air pump 8 is used, anelectrically operated type may be alternatively used.

As described above, in accordance with the invention, air to beintroduced into the exhaust pipe is not introduced during enginestarting or during starting and a predetermined time duration afterstarting, so that it is possible to prevent a decline in thepurification efficiency of the catalyst in a state in which the exhaustgas temperature immediately after starting is low.

In addition, in accordance with the invention, since the introduction ofair into the exhaust pipe is delayed until the outlet temperature of theheater increases, the temperature of the air introduced to the exhaustpipe can be set to a predetermined temperature, and it is possible toimprove the efficiency of purifying the exhaust gases.

In addition, in accordance with the invention, since heated air isintroduced into the exhaust pipe after a predetermined time durationsubsequent to engine starting, it is possible to prevent a situation inwhich the exhaust gas temperature drops due to the introduction ofnormal-temperature (unheated) air immediately after starting and thepurification efficiency of the catalyst declines. Furthermore, theamount of air introduced is varied at predetermined time intervals, sothat the purification efficiency of the catalyst can be fully exhibitedby changing the atmosphere in the reaction system of the catalyst to therich and the lean sides.

In addition, in accordance with the invention, since the exhaust gasesand the air introduced from the intake side are heated, it is possibleto increase the temperature of the exhaust gases, thereby making itpossible to improve the purification efficiency of the catalyst.

In addition, in accordance with the invention, since the heating meansin the exhaust pipe is operated even after the engine stop, it ispossible to burn the soot adhering to the interior when the exhaustgases do not flow, thereby making it possible to maintain the flow ofexhaust gases in a satisfactory manner.

In accordance with the invention, by heating the air to be introducedinto the exhaust pipe, the chemical reaction is accelerated, and byperiodically changing the amount of air introduced, the purificationefficiency of the exhaust gases can be improved.

In accordance with the invention, the time intervals at which the amountof air introduced is varied, the amount of variation, and the amount ofintroduced air heated by the heating means are varied in accordance withthe operating condition of the engine, so that the purificationefficiency of the catalyst can be controlled optimally.

In accordance with the invention, since the introduced air and thecatalyst are heated, the oxidation reaction in the catalyst isaccelerated, and the purification efficiency improves. Furthermore, theamount of air introduced is increased or decreased at predetermined timeintervals, thereby making it possible to improve the purificationefficiency.

In accordance with the invention, the amount of air heated and timeintervals of variation thereof are controlled in accordance with eitherthe exhaust gas temperature or the catalyst temperature, thereby makingit possible to prevent the deterioration due to the overheating of thecatalyst. At the same time, it is possible to optimally introduce theair in accordance with the operating condition of the engine, and theaction of purifying the exhaust gases is promoted irrespective of theoperating condition.

In accordance with this invention, the arrangement provided is such thatthe heated air is introduced in a greater amount to the upstream of thecatalyst from the starting of the engine up to the activation of thecatalyst, and the amount of air heated and introduced is changed to anamount optimally suited for the reaction of the catalyst is introducedin accordance with the activation of the catalyst. Accordingly, it ispossible to obtain activation and promotion of the catalyst, and it ispossible to obtain a large improvement in the efficiency of purificationof HC and CO which are the exhaust gas components.

Furthermore, since it becomes possible to introduce an optimum amount ofair in correspondence with the activation of the catalyst, it ispossible to suppress the amount of NOx emitted due to the oversupplystate of air to a minimum.

In accordance with the invention, the introduction of air from theintake side to the exhaust side is not effected for a predetermined timeduration subsequent to starting, so that it is possible to prevent adecline in the purification efficiency due to a drop in the catalysttemperature. In addition, since the amount of air introduced isperiodically varied, it is possible to enhance the purificationefficiency of the catalyst.

In accordance with the invention, since the introduction of air isstarted after a predetermined time duration subsequent to enginestarting, it is possible to prevent a decline in the purificationefficiency due to a drop in the catalyst temperature. In addition, sincethe amount of air introduced is periodically varied, it is possible toenhance the action of purifying the exhaust gases.

In accordance with the invention, since the exhaust gases are allowed toflow to the exhaust-gas bypass passage only during the introduction ofair, it is possible to alleviate the effect of the heat of the exhaustgases upon the heater and the like disposed in the air introducing pipeconnected to the exhaust bypass passage. Hence, the life of the heaterand the like is prolonged, and it is possible to maintain highpurification efficiency. In accordance with embodiment 3, since theintroduction of air is not effected immediately after starting, it ispossible to prevent a decline in the purification efficiency due to adrop in the catalyst temperature.

In accordance with the invention, the degree of activity of the catalystis detected by detecting the heat capacity of the catalyst, and theintroduction of air is effected when this degree of activity reaches apredetermined value, thereby making it possible to improve thepurification efficiency of the catalyst.

In accordance with the invention, the temperatures of exhaust gasesbefore and after the catalyst are detected, and when the twotemperatures have agreed with each other or have fallen within apredetermined range of values, a determination is made that the catalysthas been set in an activated state, so that air is not introduced intothe exhaust pipe. Hence, it is possible to improve the purificationefficiency after the activation of the catalyst, and it is possible toreduce the amount of nitrogen oxides emitted.

In accordance with the invention, since the air-fuel ratio sensor isdisposed in the exhaust pipe upstream of a connecting portion of the airintroducing pipe, it is possible to detecting the air-fuel ratio of theexhaust gases alone, and it is possible to accurately effect fuelcontrol during the introduction of air. In addition, since an amount ofoxygen necessary for the catalyst is detected by the oxygen sensor, andair is introduced correspondingly, it is possible to improve thepurification efficiency.

In accordance with the invention, the exhaust bypass passage is providedfor the exhaust pipe, and the exhaust gases are introduced to theexhaust bypass passage only when the air is introduced to the exhaustside, it is possible to mitigate the effect of the heat of the exhaustgases to the heater disposed in the exhaust pipe and the air introducingpipe connected to the exhaust pipe. Hence, it is possible to prolong thelife of these components, and it is possible to maintain highpurification efficiency.

In accordance with the invention, since the amount of air introduced isvaried periodically and up to its magnitude, it is possible to improvethe efficiency of purifying the exhaust gases.

In accordance with the invention, the introduction of air is not carriedout for a predetermined time duration immediately after starting, sothat it is possible to prevent a decline in the purification efficiencydue to a drop in the catalyst temperature. In addition, since theexhaust gases are allowed to flow to the exhaust bypass passage onlyduring the introduction of air to the exhaust side, it is possible toeliminate the effect of the heat of exhaust gases.

What is claimed is:
 1. An apparatus for controlling the introduction ofair into an exhaust pipe of an internal combustion engine, comprising:anair pump which introduces air into the exhaust pipe of the internalcombustion engine upstream of a catalyst; a heater which heats the airintroduced by the air pump; and a controller for: operating said airpump at the same time as said heater; introducing an amount of air fromsaid air pump which has been heated into said exhaust pipe in an amountgreater than a minimum amount of air necessary for reaction when thecatalyst is activated until the temperature of the catalyst reaches apredetermined temperature; and reducing and controlling the amount ofair introduced into said heater to the amount of air necessary for thecatalyst when the temperature of the catalyst exceeds a predeterminedtemperature.
 2. An apparatus for controlling the introduction of airinto an exhaust pipe of an internal combustion engine, comprising:an airpump which introduces air into the exhaust pipe of the internalcombustion engine upstream of a catalyst; a heater which heats the airintroduced by the air pump; and a controller for: operating said airpump at the same time as said heater; introducing an amount of air fromsaid air pump which has been heated into said exhaust pipe in an amountgreater than a minimum amount of air necessary for reaction when thecatalyst is activated until the temperature of exhaust gases downstreamof the catalyst reaches a predetermined temperature; and reducing andcontrolling the amount of air introduced into said heater to the amountof air necessary for the catalyst when the temperature of the exhaustgases downstream of the catalyst exceeds a predetermined temperature. 3.An apparatus for controlling the introduction of air into an exhaustpipe of an internal combustion engine, comprising:an air pump whichintroduces air into the exhaust pipe of the internal combustion engineupstream of a catalyst; a heater which heats the air introduced by theair pump; and a controller for: operating said air pump at the same timeas the starting of said engine; introducing heated air into said exhaustpipe at a predetermined flow rate in an amount greater than an amount ofair required when the catalyst is activated; and reducing the amount ofair introduced into said exhaust pipe after a predetermined timeduration and controlling the amount of air introduced into said exhaustpipe to the amount of air required when the catalyst is activated.
 4. Anapparatus for controlling the introduction of air into an exhaust pipeof an internal combustion engine, comprising:an air pump whichintroduces air into the exhaust pipe of the internal combustion engineupstream of a catalyst; and a controller for: operating said air pump atthe same time as the starting of said engine; introducing heated airinto said exhaust pipe at a predetermined flow rate in an amount greaterthan an amount of air required when the catalyst is activated; andchanging and controlling the amount of air introduced in accordance withthe catalyst temperature while the temperature of the catalyst is in apredetermined temperature range.
 5. An apparatus for controlling theintroduction of air into an exhaust pipe of an internal combustionengine, comprising:an air pump which introduces air into the exhaustpipe of the internal combustion engine upstream of a catalyst; and acontroller for: at the same time as the starting of said engine,introducing heated air into said exhaust pipe at a predetermined flowrate in an amount greater than an amount of air required when thecatalyst is activated; and changing and controlling the amount of airintroduced in accordance with the exhaust gas temperature while thetemperature of the exhaust downstream of the catalyst is in apredetermined temperature range.
 6. An apparatus for controlling theintroduction of air into an exhaust pipe of an internal combustionengine, comprising:an air pump which introduces air into the exhaustpipe of the internal combustion engine upstream of a catalyst; and acontroller for: operating said air pump at the same time as the startingof said engine; introducing heated air into said exhaust pipe at apredetermined flow rate in an amount greater than an amount of airrequired when the catalyst is activated; and changing and controllingthe amount of air introduced in accordance with the elapse of time froma first predetermined timing until a second predetermined timing afterthe starting of said engine.
 7. An apparatus for controlling theintroduction of air into an exhaust pipe of an internal combustionengine, comprising:an air pump which introduces air into the exhaustpipe of the internal combustion engine upstream of a catalyst; a heaterwhich heats the air introduced by the air pump; and a controller for:operating said air pump after a predetermined time duration after thestarting of said engine; introducing an amount of air from said air pumpwhich has been heated into said exhaust pipe in an amount greater than aminimum amount of air necessary for reaction when the catalyst isactivated until the temperature of the catalyst reaches a predeterminedtemperature; and reducing and controlling the amount of air introducedinto said heater to the amount of air necessary for the catalyst whenthe temperature of the catalyst exceeds a predetermined temperature. 8.An apparatus for controlling the introduction of air into an exhaustpipe of an internal combustion engine, comprising:an air pump whichintroduces air into the exhaust pipe of the internal combustion engineupstream of a catalyst; a heater which heats the air introduced by theair pump; and a controller for: operating said air pump after apredetermined time duration after the starting of said engine;introducing an amount of air from said air pump which has been heatedinto said exhaust pipe in an amount greater than a minimum amount of airnecessary for reaction when the catalyst is activated until thetemperature of exhaust gases downstream of the catalyst reaches apredetermined temperature; and reducing and controlling the amount ofair introduced into said heater to the amount of air necessary for thecatalyst when the temperature of the exhaust gases downstream of thecatalyst exceeds a predetermined temperature.
 9. An apparatus forcontrolling the introduction of air into an exhaust pipe of an internalcombustion engine, comprising:an air pump which introduces air into theexhaust pipe of the internal combustion engine upstream of a catalyst; aheater which heats the air introduced by the air pump; and a controllerfor: operating said air pump after a predetermined time durationsubsequent to the starting of said engine; introducing heated air intosaid exhaust pipe at a predetermined flow rate in an amount greater thanan amount of air required when the catalyst is activated; and reducingthe amount of air introduced into said exhaust pipe after apredetermined time duration and controlling the amount of air introducedinto said exhaust pipe to the amount of air required when the catalystis activated.
 10. An apparatus for controlling the introduction of airinto an exhaust pipe of an internal combustion engine, comprising:an airpump which introduces air into the exhaust pipe of the internalcombustion engine upstream of a catalyst; and a controller for:operating said air pump after a predetermined time duration subsequentto the starting of said engine; introducing heated air into said exhaustpipe at a predetermined flow rate in an amount greater than an amount ofair required when the catalyst is activated; and changing andcontrolling the amount of air introduced in accordance with the catalysttemperature while the temperature of the catalyst is in a predeterminedtemperature range.
 11. An apparatus for controlling the introduction ofair into an exhaust pipe of an internal combustion engine, comprising:anair pump which introduces air into the exhaust pipe of the internalcombustion engine upstream of a catalyst; and a controller for:operating said air pump after a predetermined time duration subsequentto the starting of said engine; introducing heated air into said exhaustpipe at a predetermined flow rate in an amount greater than an amount ofair required when the catalyst is activated; and changing andcontrolling the amount of air introduced in accordance with the elapseof time from a first predetermined timing until a second predeterminedtiming after the starting of said engine.